Systems and Methods for Measuring Particle Accumulation on Reactor Surfaces

ABSTRACT

Systems and methods for monitoring a particle/fluid mixture are provided. The method can include flowing a mixture comprising charged particles and a fluid past a particle accumulation probe. The method can also include measuring electrical signals detected by the probe as some charged particles pass the probe without contacting the probe while other charged particles contact the probe. The measured electrical signals can be manipulated to provide an output. The method can also include determining from the output if the charged particles contacting the probe have, on average, a different charge than the charged particles that pass the probe without contacting the probe.

BACKGROUND

In gas phase polymerization, a gaseous stream containing one or moremonomers is passed through a fluidized bed under reactive conditions inthe presence of a catalyst. A polymer product is withdrawn from thereactor, fresh monomer is introduced to the reactor to replace theremoved polymer product, and any unreacted monomer is recycled back tothe reactor. Process upsets in the reactor are often related to theaccumulation or buildup of catalyst and/or polymer particles (“particleaccumulation”) on the walls and/or other surfaces, e.g., distributionplate, within the reactor. Particle accumulation is often referred to assheeting, chunking, drooling, or plugging. When particle accumulationbecomes sufficiently large, fluidization can be disrupted, which canrequire the reactor to be shut down.

Numerous techniques are used to measure the amount of particleaccumulation and/or estimate the likelihood that particle accumulationmay occur within the reactor. One approach involves measuring the staticcharge on the catalyst/polymer being produced within the reactor. Theprincipal cause for static charge generation in the reactor isfrictional contact of dissimilar materials by a physical process knownas frictional electrification or the triboelectric effect. In gas phasepolymerization reactors, the static is generated by frictional contactbetween the catalyst and polymer particles and the reactor walls. Theobservance of static charge, however, does not necessarily andfrequently does not correspond to particle accumulation also occurringwithin the reactor and in particular catalyst particle accumulation.Conventional static charge measurement systems cannot distinguishbetween static charge present when particle accumulation is occurringand static charge present when particle accumulation is not occurring.

There is a need, therefore, for improved systems and methods formeasuring particle accumulation of catalyst and/or polymer particleswithin a polymerization reactor.

SUMMARY

Systems and methods for monitoring a particle/fluid mixture areprovided. The method can include flowing a mixture comprising chargedparticles and a fluid past a particle accumulation probe. The method canalso include measuring electrical signals detected by the probe as somecharged particles pass the probe without contacting the probe whileother charged particles contact the probe. The measured electricalsignals can be manipulated to provide an output. The method can alsoinclude determining from the output if the charged particles contactingthe probe have, on average, a different charge than the chargedparticles that pass the probe without contacting the probe.

The system for monitoring a particle/fluid mixture can include a fluidconveying structure having a flow path for flowing a mixture comprisingcharged particles and a fluid through the fluid conveying structure. Aparticle accumulation probe can be in communication with the flow pathand adapted to detect at least one electrical signal generated as thecharged particles pass the probe without contacting the probe and as thecharged particles contact the probe. An electrometer can be incommunication with the particle accumulation probe and adapted tomeasure the electrical signal detected by the probe. A processor can bein communication with the electrometer. The processor can receive themeasured electrical signal, manipulate the electrical signal, andprovide an output indicating whether the charged particles contactingthe probe are, on average, positively charged or negatively charged.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 depicts a schematic of an illustrative particle accumulationdetection system configured to detect particles segregating out of aparticle/fluid mixture.

FIG. 2 depicts a schematic of an illustrative gas phase polymerizationsystem having a particle accumulation probe configured to detectcatalyst accumulation on the inner surfaces of the polymerizationsystem.

FIG. 3 is a graphical depiction of measured entrainment static detectedby a particle accumulation probe during monitoring of a cycle fluidflowing through a gas phase polymerization reactor cycle line duringsteady state operation.

FIG. 4 is a close-up view of the graphical depiction of the absoluteautocorrelated entrainment static data shown in FIG. 3 focused on a timelag of 0 (zero) seconds.

FIG. 5 is a graphical depiction of measured entrainment static detectedby a particle accumulation probe during monitoring of a cycle fluidflowing through a gas phase polymerization reactor cycle line duringreactor startup.

FIG. 6 is a graphical depiction of the absolute autocorrelatedentrainment static data shown in FIG. 5.

FIG. 7 is a close-up view of the graphical depiction shown in FIG. 6focused on a time lag of 0 (zero) seconds.

FIG. 8 is another graphical depiction of measured entrainment staticdetected by a particle accumulation probe during monitoring of a cyclefluid flowing through a gas phase polymerization reactor cycle lineduring reactor startup.

FIG. 9 is a graphical depiction of the absolute autocorrelatedentrainment static data shown in FIG. 8.

FIG. 10 is a close-up view of the graphical depiction shown in FIG. 9focused on a time lag of 0 (zero) seconds.

DETAILED DESCRIPTION

FIG. 1 depicts a schematic of an illustrative particle accumulationdetection system 100 configured to detect particles 107, 109 separatingout of a particle/fluid mixture 105. The particle accumulation detectionsystem 100 can include one or more particle accumulation probes orsensors (one is shown) 103, electrometers (one is shown) 140, andprocessors (one is shown) 150. The particle accumulation probe or“probe” 103 can be configured to detect one or more electrical signalsor properties from charged particles (two are shown 107, 109) in aparticle/fluid mixture 105. For example, a tip 104 of the probe 103 canbe positioned or located within an internal volume 117 of a fluidconveying structure 115 such that the electrical signals or propertiesof the charged particles 107, 109 can be detected by the probe 103 asthe particle/fluid mixture 105 flows through the fluid conveyingstructure 115. As shown in FIG. 1, two separate charged particles 107,109 are depicted with each particle 107, 109 following a separate path108, 110, respectively, through the fluid conveying structure 115. Theparticles 107, 109 can each be separate or discrete particles, as shown,and/or agglomerations or aggregations of multiple particles, not shown.

The probe 103 can detect the electrical signal of the particles 107, 109as the charged particles 107, 109 approach and pass and/or approach andcontact the probe 103. For example, in following path 108, the chargedparticle 107 passes the probe 103 without contacting with the probe 103.As the particle 107 approaches the probe 103 an approaching electricalsignal or “leading lobe” can be detected via the probe tip 104. Afterthe particle 107 passes and advances away from the probe 103 a leavingelectrical signal or “lagging lobe” can be detected via the probe tip104. The detected electrical signal via line 106 can be communicated tothe electrometer 140 and then to ground. The electrometer 140 canmeasure or otherwise estimate the electrical signal detected via theprobe 103 as the particle 107 passes the probe 103. In another example,in following path 110, the charged particle 109 comes into directcontact with the probe 103. The electrical signal of the particle 109can be transferred to the probe 103. For example, the charged particle109 can transfer its charge to the probe tip 104 and the transferredcharge via line 106 can be communicated to the electrometer 140 and thento ground. The electrometer 140 can measure or otherwise estimate thecharge transferred from the particle 109 to the probe 103. In otherwords, the probe 103 can detect the one or more electrical signals ofthe particles 107 that pass the probe 103 without contacting the probe103 and the one or more electrical signals of the particles 109 thatapproach the probe 103 and contact the probe 103. As such, theelectrometer can measure or otherwise estimate the electrical signalsdetected by the probe 103 as some charged particles 107 pass the probewithout contacting the probe while other charged particles 109 contactthe probe 103.

The charged particles 107, 109 can be positively charged or negativelycharged. For example, the charged particle 107 can be positively chargedand the charged particle 109 can be negatively charged. In anotherexample, the charged particle 107 can be negatively charged and thecharged particle 109 can be positively charged. In another example, thecharged particles 107, 109 can both be positively charged or negativelycharged.

It has been surprisingly and unexpectedly discovered that the one ormore electrical signals or properties detected by the probe 103 can beused to determine whether or not the particles 107, 109 in theparticle/fluid mixture 105 are, or are likely to be, segregating out ofthe particle/fluid mixture 105 and accumulating onto an inner surface116 of the fluid conveying structure 115. It has also been surprisinglyand unexpectedly discovered that the one or more electrical signalsgenerated by particles 107 passing the probe 103, i.e. not contactingthe probe 103, can be distinguished from electrical signals generated bythe particles 109 contacting or striking the probe 103. Distinguishingbetween the particles 107 and 109, i.e. particles that pass the probe103 and particles that strike or contact the probe 103, can provide anindication as to whether or not the particles in the particle/fluidmixture 105 are, or are likely to be, segregating out of theparticle/fluid mixture and accumulating onto the inner surface 116 ofthe fluid conveying structure 115. For example, more particles 109striking the probe 103 than particles 107 passing the probe 103 canindicate that the particles are, or are likely to be, segregating out ofthe fluid particle/fluid mixture 105 and accumulating onto the innersurface 116 of the fluid conveying structure 115. In another example, ifthe particles 109 striking the probe 103 have, on average, a differentcharge than the particles 107 approaching the probe 103, suchdetermination can also indicate that the particles 109 are segregatingout of the particle/fluid mixture 105 and accumulating onto the innersurface 116 of the fluid conveying structure 115.

The probe 103 can detect both positive electrical signals and negativeelectrical signals. For example the probe 103 can be capable ofdetecting both positive current and negative current. As such, in atleast one example, the probe 103 can be referred to as a “bipolar”probe. A suitable and commercially available probe 103 can be theElectroStatic Monitor Probe (model ESM3400) available from Progression,Inc.

The electrometer 140 can measure or estimate, for example, a currentand/or voltage, detected via the probe 103. The measured current and/orvoltage can also be referred to as “entrainment static,” which is causedby the charged particles entrained or carried in the fluid. Anelectrometer 140 that detects a flow of current from the probe tip 104to ground can include, but is not limited to, an ammeter, a picoammeter(a high sensitivity ammeter), or a multi-meter. In another example, theelectrometer 140 could also detect the current flow indirectly bymeasuring or estimating a voltage generated as the current flows througha resistor. As such, the probe 103 can include any probe, sensor, orother device capable of being monitored via the electrometer 140 tomeasure, estimate, or otherwise detect one or more electrical signalssuch as current and/or voltage.

The electrometer 140 can have a response time of about 0.05 seconds(“sec”) or less, about 0.01 sec or less, about 0.009 sec or less, about0.007 sec or less, or about 0.005 sec or less. For example, theelectrometer 140 can have a response time ranging from about 0.0001 secto about 0.01 sec, about 0.001 to about 0.008 sec, or about 0.003 sec toabout 0.006 sec. The electrometer 140 can also include a 4 mA to about20 mA transmitter. The transmitter can also be capable of operating at aresponse time of from about 0.0001 sec to about 0.01 sec.

The particle accumulation probe 103 and electrometer 140 can detect andmeasure the electrical signal(s) at any desired sampling rate orfrequency. For example, the probe 103 and electrometer 140 can detectand measure the electrical signal(s) at a sampling frequency of about 90Hz, about 100 Hz, about 125 Hz, about 150 Hz, or about 200 Hz or morethan 200 Hz.

The electrical signal(s) detected via the probe 103 and measured via theelectrometer 140 can be communicated as “raw” data via line 142 to theprocessor 150. The processor 150 can manipulate the detected electricalsignal(s) or “raw” data received via in line 142 to provide an output ormanipulated electrical signal via line 152. The output in line 152 canprovide information as to one or more conditions of the particle/fluidmixture 105 within the fluid conveying structure 115. The output vialine 152 can be introduced to a display such as a monitor, an alarm, anautomated control system, or the like, or combinations thereof. Theoutput via line 152 can indicate whether or not the particles 107, 109are, or are likely to be, segregating out of the particle/fluid mixture105 and accumulating onto the inner surface(s) 116 of the of the fluidconveying structure 115. For example, the output via line 152 canindicate the charge of the particular particles that, on average,contact or strike the probe 103. Depending on the particularparticle/fluid mixture 105, positively or negatively charged particles(on average) contacting or striking the probe 103 can indicate thatparticles are accumulating onto the inner surface(s) 116 of the fluidconveying structure 115.

The processor 150 can manipulate the electrical signal or “raw” datareceived via line 142 using any desired process or combination ofprocesses. For example, the electrical signal in line 142 can undergoone or more mathematical operations to produce the output or manipulatedelectrical signal via line 152. In one example, the processor 150 canmanipulate or process the electrical signal received via line 142 fromthe electrometer 140 using the absolute autocorrelation method. Forexample, the data communicated via line 142 from the electrometer 140 tothe processor 150 can undergo a certain correlation process thatcorrelates the mean centered data. Correlation of the mean centeredelectrical signal in line 142 can provide a signal-processing toolcapable of extracting from the electrical signal in line 142 informationthat can indicate whether or not the particles 107, 109 in theparticle/fluid mixture 105 are, or are likely to be, segregating out ofthe particle/fluid mixture 105 and accumulating onto the inner surfaces116 of the fluid conveying structure 115. The output or output dataprovided via line 152 can be presented in a visually understandable formthat can be used by operational personnel, automated control systems, orthe like in controlling a system or process in which the particle/fluidmixture 105 is produced, used in, or the like.

The main or primary features of the absolute autocorrelation of ameasured electrical signal, e.g., current, in line 142, and provided asthe output via line 152, can include, but are not limited to, anapproaching curve or “leading lobe,” a leaving curve or “lagging lobe,”and a zero-lag peak or peak at zero time lag. The leading and lagginglobes can be indicative of the charge on the particles 107, as theparticles 107 approach the probe 103 and as the particles 107 pass andmove away from the probe 103, respectively. The peak at zero time lagcan be indicative of the charge on the particles 109 that strike orcontact the probe 103. A charge on the particles 109, on average, thatstrike or contact the probe 103 that is different than the charge on theparticles 107 that approach the probe 103 can indicate that theparticles 109 are segregating out of the particle/fluid mixture 105.

The correlation calculations can be performed using the function “xcorr”in the commercially available Matlab software (available from TheMathWorks). Alternatively, the correlation calculations can be performedon a computer or other processing system (e.g., processor 150)programmed in another appropriate manner. To calculate the correlationof vectors x and y (of equal size, n) using the Matlab software, thecommand “output=xcorr(x,y)” can be executed in the Matlab environment.Autocorrelation of vector x with itself is performed as a special case,using the command “output=xcorr(x).” Other suitable software that can beused to perform the absolute autocorrelation calculations can include,but are not limited to, Labview, Mathematica, and MathCad. We have founda correlation method especially useful for the analysis of data whichinvolves (i) mean centering the data vector x (by subtracting the meanof the vector from each value), (ii) computing the vector y (comprisingthe absolute values of each datum in vector x), and (iii) calculatingthe output vector z (using the correlation function z=xcorr(x,y)). Thisgeneral procedure, for the present purposes, will be referred to as“absolute autocorrelation.” The vector z (the absolute autocorrelationvector) has 2n−1 terms, with the nth term comprising the absoluteautocorrelated value corresponding to zero time lag. Covariance is awell known parameter related to autocorrelation and cross-correlation.Covariance values rather than cross correlated values can be determinedin some embodiments of the invention. Similarly, the Matlab function“detrend’ is closely related to the mean centering procedure describeabove and can be used in some embodiments of the invention.

The absolute autocorrelated data or output in line 152 can indicate ifthe average charge of the particles 107, 109 in the particle/fluidmixture 105 contacting the probe 103 is negative or positive. Dependingon the particular particle/fluid mixture 105, fluid conveying structure115, conditions, e.g. temperature and pressure, and other factors, apositive charge, on average, contacting the probe 103 can indicate thatthe particles 107 and/or 109 are (or are likely to be) accumulating ontothe inner surfaces 116 of the fluid conveying structure 115. Similarly,depending on the particular conditions, e.g., the particularparticle/fluid mixture 105, a negative charge could indicate that theparticles 107 and/or 109 are (or are likely to be) accumulating onto theinner surfaces 116 of the fluid conveying structure 115.

The particle accumulation detection system 100 can be used to monitorany process or system that includes, produces, uses, potentially couldinclude, potentially could produce, potentially could use, or otherwisecontains or could contain a charged particle/fluid mixture 105.Illustrative systems can include, but are not limited to, slurry basedpolymerization systems, solution based polymerization systems, gas phasepolymerization systems, coal gasification, catalytic reforming,catalytic cracking, cement processing, ash or carbon processingoperations, and the like.

Accordingly, the particles 107, 109 in the particle/fluid mixture 105can include polymer particles, catalyst particles, coal, ash, zeolites,and the like. The fluid can be in the gaseous phase, liquid phase, or acombination thereof. Illustrative fluids can include, but are notlimited to, hydrocarbons, e.g., alkanes and alkenes, liquid water,steam, nitrogen, carbon dioxide, carbon monoxide, hydrogen, oxygen, air,or any combination thereof.

The particle/fluid mixture 105 can also include a combination of two ormore different particles, e.g., a polymerization system or process couldinclude a particle/fluid mixture containing both polymer particles andcatalyst particles.

An exemplary process in which the particle accumulation detection systemcan be used to monitor electrical signals generated from chargedparticles in the particle/fluid mixture can be a gas phasepolymerization system. The gas phase polymerization system can use oneor more metallocene catalysts, for example, to polymerize one or moreolefins. From the measured electrical signals or data the relativeamounts of entrained solid particles (i.e. catalyst particles andpolymer particles) that pass the probe as well as strike the probe (aswell as their average charges) can be extracted from the measuredelectrical signals. For example, a current can be measured via theelectrometer and the processor can provide an output that shows theabsolute autocorrelation of the current.

The particles/fluid mixture 105 flowing past the probe 103 can be at ahigh speed, e.g. about 15 m/s, and as such, the passing and strikingevents can occur in a short period of time, e.g. less than 1 second.Additionally, there can be a substantial number of particles 107, 109interacting with the probe 103. The absolute autocorrelation methods canprovide a useful means to extract an average description of thesemultiple, fast interactions between the moving charged particles 107,109 and the probe 103. Because the interactions occur on such a shorttime scale, the interactions are observed in the absoluteautocorrelation of data in the region corresponding to a fraction of asecond lead/lag time.

As mentioned above, the primary features of the absolute autocorrelationof the measured current in line 142 and provided as the output via line152 can include a leading lobe, a lagging lobe, and a zero-lag peak orpeak at zero time lag. For a typical gas phase polymerization system,the leading lobe can be located at about −0.11 seconds and the lagginglobe can usually be a mirror image of the leading lobe and will usuallybe at about +0.11 seconds. For gas phase polymerization usingmetallocene catalyst, it has been found that the leading lobe is nearlyalways a minimum-type peak and the lagging lobe is nearly always apositive-type peak. This observation corresponds with typicalentrainment static probe measurements that indicate entrained polymerproduct usually has a negative charge. As such, the “negative” orminimum-type leading lobe usually indicates negatively charged polymerparticles approaching the probe and the lagging lobe usually indicatesthe negatively charged polymer particulates leaving or passing away fromthe probe. Accordingly, in most data reviewed for gas phasepolymerization using metallocene catalyst, the leading and lagging lobesare minima and maxima, respectively, indicating the charged particles inthe cycle gas are dominated by negatively charged polymer particles.

The peak at zero time lag describes the particles that strike the probe.Under normal or typical operations, the peaks at zero time lag areminima (just like the leading lobe). Without wishing to be bound bytheory, it is believed that this observation is due to the fact that,under typical observations, the average particle striking the probe isof the same charge sign as the average particles approaching the probe.In the context of gas phase polymerization using metallocene catalyst, asurprising and unexpected finding is the very unusual event where theleading lobe and zero time lag peak are different. For example, theleading lobe is a minimum while the zero time lag peak is a maximum.This unusual event occurs when the particles striking the probe aredifferent (on average) than the particles approaching the probe. As usedherein, the term “segregation,” refers to the event in which theparticles striking the probe are different, on average, than theparticles approaching the probe.

The ability to detect segregation is important for gas phasepolymerization processes and other processes that include or canpotentially include charged particles. In gas phase polymerization, inparticular, segregation is a known precursor to reactor shut down. Inother words, segregation of the charged metallocene catalyst (nearlyalways positively charged) from the charged polymer particles (nearlyalways negatively charged) causes agglomeration and/or fouling withinthe reactor, which leads to reactor shut down.

As the metallocene catalyst segregates from the average flow of theparticle/fluid mixture and accumulates on the probe (or any other innersurfaces such as the reactor wall and/or the inner walls of the cycleline), the concentrated deposit of active catalyst particles overheatsas polymerization reactions proceed and the polymer generated melts toform agglomerates. These hot-spots of melted polymer can increase insize by a factor of hundreds, thousands, or even tens of thousands,forming oversized agglomerations that can plug the piping, the reactor,and/or associated equipment, requiring shut down. Accordingly,determination of when catalyst particles being to segregate out of theparticle/fluid mixture provides an early warning or indicator thatagglomeration and/or fouling is occurring or about to occur within thegas phase polymerization system and corrective measures can be taken inorder to reduce the likelihood or prevent the agglomerations fromforming

The size of the particles 107, 109 can vary between different systems orprocesses and/or during operation of any particular system or process.For example, the particles 107, 109, depending on the particular processor system, can have a diameter or cross-sectional length ranging from alow of about 0.01 μm, about 0.1 μm, about 1 μm, or about 10 μm to a highof about 0.1 mm, about 1 mm, or about 5 mm. In another example, aparticular process or system can have a particle/fluid mixture 105 thatincludes two or more different particles and those two or more differentparticles can have the same average diameter or cross-sectional lengthor different average diameter or cross-sectional length. In a specificexample, in a particle/fluid mixture 105 of a polymerization system thatincludes both polymer particles and catalyst particles, the polymerparticles can have an average diameter or cross-sectional length rangingfrom a low of about 0.1 mm, about 0.5 mm, or about 1 mm to a high ofabout 2 mm, about 2.5 mm, or about 3 mm and the catalyst particles canhave an average diameter or cross-section length ranging from a low ofabout 5 μm, about 10 μm, or about 20 μm to a high of about 80 μm, about100 μm, or about 125 μm.

The particle/fluid mixture 105 can have a particle concentration rangingfrom about 0.001 percent by weight (wt %) to about 5 wt %, or from about0.01 wt % to about 1 wt %, or from about 0.05 wt % to about 0.5 wt %,based on the total weight of the particle/fluid mixture. For example,the particle concentration in the particle/fluid mixture 105 can rangefrom a low of about 0.01 wt %, about 0.05 wt %, about 0.07 wt %, orabout 0.1 wt % to a high of about 0.2 wt %, about 0.3 wt %, about 0.4 wt%, or about 0.5 wt %, based on the total weight of the particulate/fluidmixture.

The velocity of the particle/fluid mixture 105 flowing through the fluidconveying structure 115 can vary depending on the particular process orsystem. Illustrative particle/fluid mixture 105 velocities or averageflow rates through the fluid conveying structure 115 can range from alow of about 1 m/s, about 5 m/s, about 10 m/s or about 15 m/s to a highof about 20 m/s, about 30 m/s, about 40 m/s, or about 50 m/s. Forexample, a gas phase polymerization system can have a particle/fluidmixture flowing from a top of a polymerization reactor, through a cycleor recycle line, and to the bottom of the polymerization reactor, with avelocity typically ranging from about 5 m/s to about 30 m/s, or fromabout 10 m/s to about 20 m/s, or from about 12 m/s to about 18 m/s.

Depending on the particular system or process, the particle/fluidmixture 105 can be monitored via the particle accumulation detectionsystem 100 within a number of different types of fluid conveyingstructures. Illustrative fluid conveying structures 115 can include, butare not limited to, pipes, tubes, hoses, reactors, e.g., polymerizationreactors, fluidized catalytic reactors, and the like, ducts, conduits,exhaust or vent stacks, transfer or transportation pipes or pipelines,and the like. For example, the fluid conveying structure 115 can be agas phase polymerization reactor and/or one or more process linesassociated with the gas phase polymerization reactor, such as a cyclefluid line, a product recovery line, and/or a vent line.

FIG. 2 depicts a schematic of an illustrative gas phase polymerizationsystem 200 having a particle accumulation probe 103 configured to detectcatalyst accumulation on the inner surfaces of the polymerization system200. The polymerization system 200 can include one or morepolymerization reactors 201, discharge tanks 255 (only one shown),recycle compressors 270 (only one shown), and heat exchangers 275 (onlyone shown). The polymerization system 200 can include more than onereactor 201 arranged in series, parallel, or configured independent fromthe other reactors, each reactor having its own associated dischargetanks 255, recycle compressors 270, and heat exchangers 275 oralternatively, sharing any one or more of the associated discharge tanks255, recycle compressors 270, and heat exchangers 275. For simplicityand ease of description, embodiments of the invention will be furtherdescribed in the context of a single reactor train.

The reactor 201 can include a cylindrical section 203, a transitionsection 205, and a velocity reduction zone or dome 207. The cylindricalsection 203 is disposed adjacent the transition section 205. Thetransition section 205 can expand from a first diameter that correspondsto the diameter of the cylindrical section 203 to a larger diameteradjacent the dome 207. The location or junction at which the cylindricalsection 203 connects to the transition section 205 can be referred to asthe “neck” or the “reactor neck” 204.

The cylindrical section 203 can include a reaction zone 212. Thereaction zone can be a fluidized reaction bed or fluidized bed. In oneor more embodiments, a distributor plate 219 can be disposed within thecylindrical section 203, generally at or toward the end of thecylindrical section that is opposite the end adjacent to the transitionsection 205. The reaction zone 212 can include a bed of growing polymerparticles, formed polymer particles and catalyst particles fluidized bythe continuous flow of polymerizable and modifying gaseous components inthe form of make-up feed and recycle fluid through the reaction zone212.

One or more cycle fluid lines 215 and vent lines 218 can be in fluidcommunication with the top head 207 of the reactor 201. A polymerproduct can be recovered via line 217 from the reactor 201. A reactorfeed via line 210 can be introduced to the polymerization system 200 atany location or combination of locations. For example, the reactor feedvia line 210 can be introduced to the cylindrical section 203, thetransition section 205, the velocity reduction zone 207, to any pointwithin the cycle fluid line 215, or any combination thereof. Preferably,the reactor feed 210 is introduced to the cycle fluid in line 215 beforeor after the heat exchanger 275. A catalyst feed via line 213 can beintroduced to the polymerization system 200 at any point. Preferably thecatalyst feed via line 213 is introduced to a fluidized bed 212 withinthe cylindrical section 203.

The particle accumulation probe 103 can be in communication with thepolymerization system 200 at any number of locations. As shown in FIG.2, a probe 103 is in communication with the cycle line 215 between thereactor 201 and the heat exchanger 275. Other suitable locations theprobe 103 can be in communication with the polymerization system 200 caninclude, but are not limited to, the cylindrical section 203, transitionsection 205, and dome 207. For example, the probe 103 can be incommunication with the cylindrical section 203 between an inlet of thecycle line 215 to the reactor 201 and the distributor plate 219 orbetween the distributor plate 219 and the transition section 205. Inanother example, the probe 103 can be in communication with the cycleline 215 between the heat exchanger 275 and the compressor 270. Theprobe 103 can also be in communication with the cycle line 215 betweenthe dome 207 of the reactor 201 and the compressor 270.

Any number of probes 103 can be in communication with the polymerizationsystem 200. For example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more probes103 can be in communication with the polymerization system 200. If twoor more probes 103 are in communication with the polymerization system200, the two or more probes 103 can be disposed about differentlocations, the same or similar locations, or a combination of differentand similar locations.

If two or more probes 103 are in communication with the polymerizationsystem 200, the two or more probes 103 can communicate the detectedelectrical signal(s) via line 106 to a single electrometer 140. Inanother example, if two or more probes 103 are in communication with thepolymerization system 200, the two or more probes 103 can communicatethe detected electrical signal(s) via line 106 to separate orindependent electrometers 140. In still another example, multiple probes103 can communicate the detected electrical signal(s) via line 106 to asingle electrometer 140 and one or more other probes 103 can communicatethe detected electrical signal(s) via line 106 to separate electrometers140. Similarly, any number of processors 150 can be used to manipulatethe data provided via line 142 from one or more electrometers 140.

The particle accumulation probe 103 can be used during predetermined orselected polymerization process periods, continuously, randomly, or anycombination thereof. For example, the particle accumulation probe 103can be used to detect one or more electrical signals generated by thepassing and/or contacting particles 107, 109 during polymerizationreactor start-up. Polymerization reactor start-up can be a particularlysensitive process time period because catalyst-rich accumulations ontothe inner surfaces of the polymerization system 200, e.g., reactor 201,cycle line 215, and the like, are more likely to occur. When catalystparticles accumulate onto the inner surfaces of the polymerizationsystem 200 hot spots form and can cause polymer particles to melt andfuse. The melted and/or fused polymer particles are the precursor tosheeting, chunking, drooling, plugging, and the like. The agglomerationscan occur on the inner surfaces of the cylindrical section 203,transition section 205, dome 207, cycle line 215, below the distributorplate 219, within the heat exchanger 271, and the like. The occurrenceof such agglomerations or fouling can be especially prone when usingmetallocene catalyst because much higher levels of static are generatedin contrast to other polymerization catalysts such as Ziegler-Nattacatalysts. Other polymerization process time periods that can be moreprone to agglomeration or fouling can include transition periods, i.e.when transition between one polymer product to another polymer productis made, super-condensed mode operation, entering condensed modeoperation, operation at low condensing levels, loss of fluidized bedlevel control, and the like.

Accordingly, the particle accumulation probe 103 can be selectivelyoperated during predetermined process time periods, such aspolymerization reactor start-up. In another example, the particleaccumulation probe 103 can be continuously or substantially continuouslyoperated during operation of the polymerization system 200.

One particularly desirable polymerization process time period that theprobe 103 can be used to detect the electrical signal(s) of the passingand/or contacting particles 107, 109 is polymerization reactor start-up.Fouling of the distributor plate 219 during polymerization reactorstart-up is commonly referred to as “hyperfouling.” Hyperfouling startswith catalyst particles (or catalyst-rich particles) segregating out ofthe cycle gas and accumulating onto the inner surfaces of the reactor201, cycle line 215, and the like. Entrainment static is virtuallyalways observed during polymerization start-up. However, not allentrainment static results in hyperfouling.

For example, entrainment static generated by the particles in the cyclefluid flowing through the cycle line 215 and detected via the probe 103can be large, e.g., +/−200 nano-amps (nA, instantaneous) or even +/−400nA, instantaneous, but no hyperfouling occurs. At other times, thecurrent or entrainment static generated by the particles in the cyclefluid flowing through the cycle line 215 and detected via the probe 103can be large and hyperfouling does occur. Probability dictates that thecharged particles, i.e. polymer particles and catalyst particles, willboth strike or contact the probe 103 as the charged particles flowtoward the probe. Without wishing to be bound by theory, it is believedthat when number of charged particles contacting the probe 103, onaverage, are catalyst particles, conditions within the polymerizationsystem 200 are such that catalyst segregation from the particle/fluidmixture 105 is occurring or is likely to occur. Similarly, it isbelieved that when the number of charged particles contacting the probe103, on average, are polymer particles, conditions within thepolymerization system 200 are such that the catalyst particles are notsegregating out of the particle/fluid mixture 105, at least not in asufficient amount to cause catalyst accumulation that tends to or islikely to lead to hyperfouling and other polymer agglomerations withinthe polymerization system 200.

Accordingly, and without wishing to be bound by theory, it is believedthat process conditions should be adjusted when the average number ofcharged particles striking the probe 103 are catalyst particles in orderto prevent hyperfouling during polymerization startup. Additionally,from experiment and observation it has been found that forpolymerization with metallocene catalyst, the catalyst particles arepositively charged and the polymer particles are negatively charged. Assuch, observation of an average number of positively charged particlescontacting the probe 103 from the absolute autocorrelated data can beinterpreted to indicate that the catalyst particles are segregating outof the cycle fluid and accumulating onto the inner surfaces of thepolymerization system. In other systems, however, observation of anaverage number of negatively charged particles contacting the probe 103,as indicated by the absolute autocorrelated data, can indicate that thecatalyst particles are segregating out of the cycle fluid andaccumulating onto the inner surfaces of the polymerization system. Assuch, depending on the particular polymerization reaction conditions theparticular observation, i.e. average number of particle strikes arepositive or negative, could indicate catalyst particle accumulation ontothe inner surfaces of the polymerization system 200.

If an undesired amount or degree of catalyst particles are estimated tobe accumulating or likely to begin accumulating onto the inner surfacesof the polymerization system 200, e.g., the inner surfaces of thereactor 201, cycle line 215, and the like, one or more operationaladjustments or steps can be taken to reduce the accumulation of ortendency for the particles to accumulate. For example, one or morecontinuity additives and/or antistatic agents can be introduced to thereactor 201 to reduce the level of static charge on the polymer producttherein. In another example, a rate of catalyst and/or feed introductioncan be adjusted or modified, e.g., increased or decreased. In stillanother example, the reactor 201 can be idled for a period of time, i.e.polymerization can be stopped within the reactor 201, but fluids cancontinue to cycle therein and a non-reacting fluidized bed can bemaintained within the reactor during idling. Illustrative idlingtechniques can include those discussed and described in U.S. ProvisionalPatent Application having Ser. No. 60/305623. In yet another example,the reactor 201 can be shut down or “killed.” Other actions oradjustments that can be taken to reduce the amount of charge on thepolymer product within the reactor 201 can also include, but are notlimited to, replacing a source of the catalyst introduced via line 213to the reactor 201 with a different source of the catalyst, changing thetype of catalyst introduced via line 213 to the reactor 201, adjusting aconcentration of any condensing agents, if used, within the reactor 201,transitioning the polymerization reactor 201 to produce a differentpolymer product, and the like. Any one or more operational adjustmentsor steps can be taken alone, in any combination, and/or in any order toreduce the amount of charge on the polymer product within the reactor201.

Other illustrative techniques that can also be used to reduce oreliminate catalyst particle accumulation on the inner surfaces of thepolymerization system 200 can include the introduction of finely dividedparticulate matter to prevent agglomeration, as described in U.S. Pat.Nos. 4,994,534 and 5,200,477. Condensing mode operation, such asdisclosed in U.S. Pat. Nos. 4,543,399 and 4,588,790 can also be used toassist in heat removal from the fluid bed polymerization reactor.

Introducing continuity additive(s) can include the addition of negativecharge generating chemicals to balance positive voltages or the additionof positive charge generating chemicals to neutralize negative voltagepotentials as described in U.S. Pat. No. 4,803,251. Antistaticsubstances can also be added, either continuously or intermittently toprevent or neutralize electrostatic charge generation. The continuityadditive and/or antistatic substances, if used, can be introduced withthe feed via line 210, the catalyst via line 213, a separate inlet (notshown), or any combination thereof.

The continuity additive can interact with the particles and othercomponents in the fluidized bed. For example, the continuity additivecan reduce or neutralize static charges related to frictionalinteraction of the catalyst and polymer particles. The continuityadditive can also react or complex with various charge-containingcompounds that can be present or formed in the reactor. The continuityadditive can also react or complex with oxygenates and other catalystpoisons. The continuity additive can also be referred to as a staticcontrol agent.

As used herein, the term “continuity additive” refers to a compound orcomposition that when introduced into a gas phase fluidized bed reactorcan influence or drive the static charge (negatively, positively, or tozero) in the fluidized bed. The continuity additive or combination ofcontinuity additives can depend, at least in part, on the nature of thestatic charge. The particular continuity additive or combination ofcontinuity additives can depend, at least in part, on the particularpolymer being produced within the polymerization reactor, the particularspray dried catalyst system or combination of catalyst systems beingused, or a combination thereof. Suitable continuity additives and usesthereof can be as discussed and described in European Patent No. 0 229368; U.S. Pat. Nos. 5,283,278; 4,803,251; and 4,555,370; and WOPublication No. WO2009/023111; and WO01/44322.

Continuing with reference to FIG. 2, in general, the height to diameterratio of the cylindrical section 203 can vary in the range of from about2:1 to about 5:1. The range, of course, can vary to larger or smallerratios and depends, at least in part, upon the desired productioncapacity and/or reactor dimensions. The cross-sectional area of the dome207 is typically within the range of from about 2 to about 3 multipliedby the cross-sectional area of the cylindrical section 203.

The velocity reduction zone or dome 207 has a larger inner diameter thanthe cylindrical section 203. As the name suggests, the velocityreduction zone 207 slows the velocity of the gas due to the increasedcross-sectional area. This reduction in gas velocity allows particlesentrained in the upward moving gas to fall back into the bed, allowingprimarily only gas to exit overhead of the reactor 201 through the cyclefluid line 215. The cycle fluid recovered via line 215 can contain lessthan about 10% wt, less than about 8% wt, less than about 5% wt, lessthan about 4% wt, less than about 3% wt, less than about 2% wt, lessthan about 1% wt, less than about 0.5% wt, or less than about 0.2% wt ofthe particles entrained in fluidized bed 212. In another example, thecycle fluid recovered via line 215 can have a particle concentrationranging from a low of about 0.001 wt % to about 5 wt %, from about 0.01wt % to about 1 wt %, or from about 0.05 wt % to about 0.5 wt %, basedon the total weight of the particle/cycle fluid mixture in line 215. Forexample, the particle concentration in the cycle fluid in line 215 canrange from a low of about 0.01 wt %, about 0.05 wt %, about 0.07 wt %,or about 0.1 wt % to a high of about 0.5 wt %, about 1.5 wt %, about 3wt %, or about 4 wt %, based on the total weight of the cycle fluid andparticles in line 215.

Suitable gas phase polymerization processes for producing the polymerproduct via line 217 are described in U.S. Pat. Nos. 3,709,853;4,003,712; 4,011,382; 4,302,566; 4,543,399; 4,588,790; 4,882,400;5,028,670; 5,352,749; 5,405,922; 5,541,270; 5,627,242; 5,665,818;5,677,375; 6,255,426; European Patent Nos. EP 0802202; EP 0794200; EP0649992; EP 0634421. Other suitable polymerization processes that can beused to produce the polymer product can include, but are not limited to,solution, slurry, and high pressure polymerization processes. Examplesof solution or slurry polymerization processes are described in U.S.Pat. Nos. 4,271,060; 4,613,484; 5,001,205; 5,236,998; and 5,589,555.

The reactor feed in line 210 can include any polymerizable hydrocarbonof combination of hydrocarbons. For example, the reactor feed can be anyolefin monomer including substituted and unsubstituted alkenes havingtwo to 12 carbon atoms, such as ethylene, propylene, 1-butene,1-pentene, 1-hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene,1-dodecene, 1-hexadecene, and the like. The reactor feed can alsoinclude non-hydrocarbon gas(es) such as nitrogen and/or hydrogen. Thereactor feed can enter the reactor at multiple and different locations.For example, monomers can be introduced into the fluidized bed invarious ways including direct injection through a nozzle (not shown)into the fluidized bed. The polymer product can thus be a homopolymer ora copolymer, including a terpolymer, having one or more other monomericunits. For example, a polyethylene product could include at least one ormore other olefin(s) and/or comonomer(s).

The reactor feed in line 210 can also include the one or more modifyingcomponents such as one or more induced condensing agents (“ICAs”).Illustrative ICAs include, but are not limited to, propane, butane,isobutane, pentane, isopentane, hexane, isomers thereof, derivativesthereof, and combinations thereof. The ICAs can be introduced to providea reactor feed to the reactor having an ICA concentration ranging from alow of about 1 mol %, about 5 mol %, or about 10 mol % to a high ofabout 25 mol %, about 35 mol %, or about 45 mol %. Typicalconcentrations of the ICAs can range from about 14 mol %, about 16 mol%, or about 18 mol % to a high of about 20 mol %, about 22 mol %, orabout 24 mol %. The reactor feed can include other non-reactive gasessuch as nitrogen and/or argon. Further details regarding ICAs can be asdiscussed and described in U.S. Pat. Nos. 5,352,749; 5,405,922;5,436,304; and 7,122,607; and WO Publication No. 2005/113615(A2).

The catalyst feed in line 213 can include any catalyst or combination ofcatalysts. Illustrative catalysts can include, but are not limited to,Ziegler-Natta catalysts, chromium-based catalysts, metallocene catalystsand other single-site catalysts including Group 15-containing catalysts,bimetallic catalysts, and mixed catalysts. The catalyst can also includeAlCl₃, cobalt, iron, palladium, chromium/chromium oxide or “Phillips”catalysts. Any catalyst can be used alone or in combination with anyother catalyst.

Suitable metallocene catalyst compounds can include, but are not limitedto, metallocenes described in U.S. Pat. Nos. 7,179,876; 7,169,864;7,157,531; 7,129,302; 6,995,109; 6,958,306; 6,884,748; 6,689,847;5,026,798; 5,703,187; 5,747,406; 6,069,213; 7,244,795; 7,579,415; U.S.Patent Application Publication No. 2007/0055028; and WO Publications WO97/22635; WO 00/699/22; WO 01/30860; WO 01/30861; WO 02/46246; WO02/50088; WO 04/022230; WO 04/026921; and WO 06/019494.

The “Group 15-containing catalyst” may include Group 3 to Group 12 metalcomplexes, wherein the metal is 2 to 8 coordinate, the coordinatingmoiety or moieties including at least two Group 15 atoms, and up to fourGroup 15 atoms. For example, the Group 15-containing catalyst componentcan be a complex of a Group 4 metal and from one to four ligands suchthat the Group 4 metal is at least 2 coordinate, the coordinating moietyor moieties including at least two nitrogens. Representative Group15-containing compounds are disclosed in WO Publication No. WO 99/01460;European Publication Nos. EP0893454A1; EP 0894005A1; U.S. Pat. Nos.5,318,935; 5,889,128; 6,333,389; and 6,271,325.

Illustrative Ziegler-Natta catalyst compounds are disclosed in EuropeanPatent Nos. EP 0103120; EP 1102503; EP 0231102; EP 0703246; U.S. Pat.Nos. RE 33,683; 4,115,639; 4,077,904; 4,302,565; 4,302,566; 4,482,687;4,564,605; 4,721,763; 4,879,359; 4,960,741; 5,518,973; 5,525,678;5,288,933; 5,290,745; 5,093,415; and 6,562,905; and U.S. PatentApplication Publication No. 2008/0194780. Examples of such catalystsinclude those comprising Group 4, 5 or 6 transition metal oxides,alkoxides and halides, or oxides, alkoxides and halide compounds oftitanium, zirconium or vanadium; optionally in combination with amagnesium compound, internal and/or external electron donors (alcohols,ethers, siloxanes, etc.), aluminum or boron alkyl and alkyl halides, andinorganic oxide supports.

Suitable chromium catalysts can include di-substituted chromates, suchas CrO₂(OR)₂; where R is triphenylsilane or a tertiary polyalicyclicalkyl. The chromium catalyst system may further include CrO₃,chromocene, silyl chromate, chromyl chloride (CrO₂Cl₂),chromium-2-ethyl-hexanoate, chromium acetylacetonate (Cr(AcAc)₃), andthe like. Other non-limiting examples of chromium catalysts aredescribed in U.S. Pat. No. 6,989,344.

The mixed catalyst can be a bimetallic catalyst composition or amulti-catalyst composition. As used herein, the terms “bimetalliccatalyst composition” and “bimetallic catalyst” include any composition,mixture, or system that includes two or more different catalystcomponents, each having a different metal group. The terms“multi-catalyst composition” and “multi-catalyst” include anycomposition, mixture, or system that includes two or more differentcatalyst components regardless of the metals. Therefore, the terms“bimetallic catalyst composition,” “bimetallic catalyst,”“multi-catalyst composition,” and “multi-catalyst” will be collectivelyreferred to herein as a “mixed catalyst” unless specifically notedotherwise. In one example, the mixed catalyst includes at least onemetallocene catalyst component and at least one non-metallocenecomponent.

In some embodiments, an activator may be used with the catalystcompound. As used herein, the term “activator” refers to any compound orcombination of compounds, supported or unsupported, which can activate acatalyst compound or component, such as by creating a cationic speciesof the catalyst component. Illustrative activators include, but are notlimited to, aluminoxane (e.g., methylaluminoxane “MAO”), modifiedaluminoxane (e.g., modified methylaluminoxane “MMAO” and/ortetraisobutyldialuminoxane “TIBAO”), and alkylaluminum compounds,ionizing activators (neutral or ionic) such as tri(n-butyl)ammoniumtetrakis(pentafluorophenyl)boron may be also be used, and combinationsthereof.

The catalyst compositions can include a support material or carrier. Asused herein, the terms “support” and “carrier” are used interchangeablyand are any support material, including a porous support material, forexample, talc, inorganic oxides, and inorganic chlorides. The catalystcomponent(s) and/or activator(s) can be deposited on, contacted with,vaporized with, bonded to, or incorporated within, adsorbed or absorbedin, or on, one or more supports or carriers. Other support materials caninclude resinous support materials such as polystyrene, functionalizedor crosslinked organic supports, such as polystyrene divinyl benzenepolyolefins or polymeric compounds, zeolites, clays, or any otherorganic or inorganic support material and the like, or mixtures thereof.

Suitable catalyst supports are described in U.S. Pat. Nos. 4,701,432,4,808,561; 4,912,075; 4,925,821; 4,937,217; 5,008,228; 5,238,892;5,240,894; 5,332,706; 5,346,925; 5,422,325; 5,466,649; 5,466,766;5,468,702; 5,529,965; 5,554,704; 5,629,253; 5,639,835; 5,625,015;5,643,847; 5,665,665; 5,698,487; 5,714,424; 5,723,400; 5,723,402;5,731,261; 5,759,940; 5,767,032; 5,770,664; and 5,972,510; and WOPublication Nos. WO 95/32995; WO 95/14044; WO 96/06187; WO 97/02297; WO99/47598; WO 99/48605; and WO 99/50311.

The cycle fluid via line 215 can be compressed in the compressor 270 andthen passed through the heat exchanger 275 where heat can be exchangedbetween the cycle fluid and a heat transfer medium. For example, duringnormal operating conditions a cool or cold heat transfer medium via line271 can be introduced to the heat exchanger 275 where heat can betransferred from the cycle fluid in line 215 to produce a heated heattransfer medium via line 277 and a cooled cycle fluid via line 215. Inanother example, during idling of the reactor 201 a warm or hot heattransfer medium via line 271 can be introduced to the heat exchanger 275where heat can be transferred from the heat transfer medium to the cyclefluid in line 215 to produce a cooled heat transfer medium via line 217and a heated cycle fluid via line 215. The terms “cool heat transfermedium” and “cold heat transfer medium” refer to a heat transfer mediumhaving a temperature less than the fluidized bed 212 within the reactor201. The terms “warm heat transfer medium” and “hot heat transfermedium” refer to a heat transfer medium having a temperature greaterthan the fluidized bed 212 within the reactor 201. The heat exchanger275 can be used to cool the fluidized bed 212 or heat the fluidized bed212 depending on the particular operating conditions of thepolymerization system 200, e.g. start-up, normal operation, and shutdown. Illustrative heat transfer mediums can include, but are notlimited to, water, air, glycols, or the like. It is also possible tolocate the compressor 270 downstream from the heat exchanger 275 or atan intermediate point between several heat exchangers 275.

After cooling, all or a portion of the cycle fluid in line 215, thecycle fluid can be returned to the reactor 201. The cooled cycle fluidin line 215 can absorb the heat of reaction generated by thepolymerization reaction. The heat exchanger 275 can be of any type ofheat exchanger. Illustrative heat exchangers can include, but are notlimited to, shell and tube, plate and frame, U-tube, and the like. Forexample, the heat exchanger 275 can be a shell and tube heat exchangerwhere the cycle fluid via line 215 can be introduced to the tube sideand the heat transfer medium can be introduced to the shell side of theheat exchanger 275. If desired, to or more heat exchangers can beemployed, in series, parallel, or a combination of series and parallel,to lower or increase the temperature of the cycle fluid in stages.

Preferably, the cycle gas via line 215 is returned to the reactor 201and to the fluidized bed 212 through the fluid distributor plate(“plate”) 219. The plate 219 can prevent polymer particles from settlingout and agglomerating into a solid mass. The plate 219 can also preventor reduce the accumulation of liquid at the bottom of the reactor 201.The plate 219 can also facilitate transitions between processes whichcontain liquid in the cycle stream 215 and those which do not and viceversa. Although not shown, the cycle gas via line 215 can be introducedinto the reactor 201 through a deflector disposed or locatedintermediate an end of the reactor 201 and the distributor plate 219.Illustrative deflectors and distributor plates suitable for this purposeare described in U.S. Pat. Nos. 4,877,587; 4,933,149; and 6,627,713.

The catalyst feed via line 213 can be introduced to the fluidized bed212 within the reactor 201 through one or more injection nozzles (notshown) in fluid communication with line 213. The catalyst feed ispreferably introduced as pre-formed particles in one or more liquidcarriers (i.e. a catalyst slurry). Suitable liquid carriers can includemineral oil and/or liquid or gaseous hydrocarbons including, but notlimited to, propane, butane, isopentane, hexane, heptane octane, ormixtures thereof. A gas that is inert to the catalyst slurry such as,for example, nitrogen or argon can also be used to carry the catalystslurry into the reactor 201. In one example, the catalyst can be a drypowder. In another example, the catalyst can be dissolved in a liquidcarrier and introduced to the reactor 201 as a solution. The catalystvia line 213 can be introduced to the reactor 201 at a rate sufficientto maintain polymerization of the monomer(s) therein.

The polymer product via line 217 can be discharged from the reactor 201by opening valve 257 while valves 259, 267 are in a closed position.Product and fluid enter the product discharge tank 255. Valve 257 isclosed and the product is allowed to settle in the product dischargetank 255. Valve 259 is then opened permitting fluid to flow via line 261from the product discharge tank 255 to the reactor 240. In anotherexample, the separated fluid in line 261 can be introduced to the cycleline 215. The separated fluid in line 261 can include unreactedmonomer(s), hydrogen, ICA(s), and/or inerts. Valve 259 can then beclosed and valve 267 can be opened and any product in the productdischarge tank 255 can flow out of the discharge tank 255. Valve 267 canthen be closed. Although not shown, the polymer product via line 268 canbe introduced to a plurality of purge bins or separation units, inseries, parallel, or a combination of series and parallel, to furtherseparate gases and/or liquids from the product. The particular timingsequence of the valves 257, 259, 267, can be accomplished by use ofconventional programmable controllers which are well known in the art.

Another product discharge system which can be alternatively employed isthat disclosed in U.S. Pat. No. 4,621,952. Such a system employs atleast one (parallel) pair of tanks comprising a settling tank and atransfer tank arranged in series and having the separated gas phasereturned from the top of the settling tank to a point in the reactornear the top of the fluidized bed. Other suitable product dischargesystems are described in PCT Publications WO2008/045173 andWO2008/045172.

The reactor 201 can be equipped with one or more vent lines 218 to allowventing the bed during start up, operation, and/or shut down. Thereactor 201 can be free from the use of stirring and/or wall scraping.The cycle line 215 and the elements therein (compressor 270, heatexchanger 275) can be smooth surfaced and devoid of unnecessaryobstructions so as not to impede the flow of cycle fluid or entrainedparticles.

The conditions for polymerization vary depending upon the monomers,catalysts, catalyst systems, and equipment availability. The specificconditions are known or readily derivable by those skilled in the art.For example, the temperatures can be within the range of from about −10°C. to about 140° C., often about 15° C. to about 120° C., and more oftenabout 70° C. to about 110° C. Pressures can be within the range of fromabout 10 kPag to about 10,000 kPag, such as about 500 kPag to about5,000 kPag, or about 1,000 kPag to about 2,200 kPag, for example.Additional details of polymerization can be found in U.S. Pat. No.6,627,713.

In addition to the particle accumulation probe 103, various othersystems and/or methods can be used to monitor and/or control a degree orlevel of fouling within the reactor 201. For example, if thepolymerization system 200 is operated in condensed mode, a commontechnique for monitoring the polymerization can include monitoring astickiness control parameter, such as a reduced melt initiationtemperature or “dMIT” value, which can provide an estimate as to thedegree of polymer stickiness within the reactor 201. Another method formonitoring polymerization can include estimating acoustic emissionswithin the reactor 201, which can also provide an estimate as to thedegree of polymer stickiness within the reactor 201. Additional detailsof monitoring a stickiness control parameter can be as discussed anddescribed in U.S. Patent Application Publication No. 2008/0065360 andPCT Publication WO2008/030313. Another method for monitoringpolymerization can include estimating acoustic emissions within thereactor, which can also provide an estimate as to the degree of polymerstickiness within the reactor. Additional details of monitoring apolymerization reactor via acoustic emissions are described in U.S.Publication No. 2007/0060721.

EXAMPLES

To provide a better understanding of the foregoing discussion, thefollowing non-limiting examples are provided. Although the examples aredirected to specific embodiments, they are not to be viewed as limitingthe invention in any specific respect.

Data acquired during a gas phase polymerization reactor operating understeady state conditions is shown in FIGS. 3 and 4 (Example 1). Dataacquired during a gas phase polymerization reactor startup in which nohyperfouling was observed is shown in FIGS. 5-7 (Example 2). Dataacquired during a polymerization reactor startup in which hyperfoulingwas observed, is shown in FIGS. 8-10 (Example 3).

The particle accumulation probe used for measuring the current(“entrainment static”) in all examples was a Progression Correflux model3400 with custom “fast,” “bipolar” electronics capable of 5 millisecondresponse. The model 3400 probe was mounted in a gas phase reactor systemof the type described in FIG. 2, where the probe was mounted on thereactor cycle gas system, approximately 5 meters downstream of thecompressor. The probe extended about 18 inches into a 36 inch diametercycle pipe (to the centerline of the pipe). An integral housing locatedoutside the flange contained the electrometer and a high-speedtransmitter. The electronics were shielded to eliminate outside strayelectromagnetic fields from interfering with the probe.

The particle accumulation probe sampled the entrainment static data at100 Hz for a period of 5 minutes for all examples. As such, the numberof data points acquired over the 5 minutes was equal to 30,000 datapoints. The measured electric current for all examples was acquiredduring polymerization start-up for a gas phase polymerization system.

The measured entrainment static data for all examples was introduced toa processor configured to operate the software program Matlab (availablefrom The MathWorks). The Matlab function “xcorr” was used to manipulatethe measured entrainment static using the absolute autocorrelationmethodology for entrainment static data measured via the electrometer.

Referring to Example 1, FIG. 3 is a graphical depiction of the measuredentrainment static detected by a particle accumulation probe duringmonitoring of a cycle fluid flowing through a gas phase polymerizationreactor cycle line during steady state operation. FIG. 4 is a close-upview of the graphical depiction of the absolute autocorrelatedentrainment static data shown in FIG. 3 focused on a time lag of 0(zero) seconds. The data shown in FIGS. 3 and 4 is representative ofdata acquired during numerous, typical gas phase polymerization reactorswhile operating under steady state conditions. In other words, Example 1is provided to illustrate typical data acquired from gas phasepolymerization reactors operating under a range various processconditions and parameters, e.g., varying reactor temperatures,pressures, feed rates, reactants, and the like.

As shown in FIG. 4, the leading lobe 403 was located at about −0.11seconds and was a “negative” or minimum type peak. The lagging lobe 410was essentially a mirror image of the leading lobe 403 and occurred atabout +0.11 seconds and was a “positive” or maximum type peak. The peakat zero time lag 405 was also a “negative” or minimum type peak as theleading lobe 403. Since the leading lobe 403 and the peak at zero timelag 405 are both minima, it can be inferred that the average particlestriking the probe was of the same charge sign as the average particleapproaching the probe. Accordingly, Example 1 shows a typical gas phasepolymerization reactor operating under normal, non-fouling conditions,steady state conditions in which catalyst particles were not found to besegregating out of the particle/fluid mixture flowing through the cycleline.

Referring to Example 2, FIG. 5 is a graphical depiction of measuredentrainment static detected by the particle accumulation probe duringmonitoring of a cycle fluid flowing through a gas phase polymerizationreactor cycle line. The time at which the catalyst was introduced to thepolymerization reactor was around 0.5×10⁴ data points on the x-axis orabout 50 seconds after measurement of the electric current began.

The polymer product in Example 2 was prepared by polymerizing ethyleneand hexene in a gas phase polymerization reactor. The polymer productwas produced using a metallocene catalyst. The gas composition withinthe reactor was about 57.1 mol % ethylene, about 0.95 mol % hexene,about 0.02 mol % hydrogen, about 35.1 mol % nitrogen, and about 7.0 mol% isopentane (used as and Induced Condensing Agent, ICA). The ethylenepartial pressure was about 151.8 psia. The reactor was operated at atemperature of about 181° F. and a pressure of about 263 psig. Since thedata was acquired during reactor start-up, none of the isopentane wascondensed. The superficial gas velocity of the cycle gas through thepolymerization reactor was about 2.3 ft/s. After introduction of thecatalyst (approximately the 0.5×10⁴ data point) a general increase orwidening of static detected by the particle accumulation probe wasobserved and is clearly shown as a widening of the measured static shownin FIG. 5.

FIG. 6 is a graphical depiction of the absolute autocorrelatedentrainment static data shown in FIG. 5. The absolute autocorrelateddata graphically depicted in FIG. 6 shows that an average charge of thecharged particles in the cycle fluid was negatively charged. Fromexperimental observation and experience, negative charges in aparticle/fluid mixture of a gas phase polymerization process using ametallocene catalyst is generated from polymer particles. In otherwords, the polymer particles in a gas phase polymerization cycle fluidare negatively charged. As such, the dominant charge measured via theelectrometer was generated by negatively charged polymer particles.

FIG. 7 is a close-up view of the graphical depiction shown in FIG. 6focused on a time lag of 0 (zero) seconds. At zero time lag there was aweak signal 705, which indicates that relatively few charged particlesstruck the probe. The zero-lag signal 705 is small and was within theband of y-axis values defined by the minima and maxima of the leadinglobe 703 and lagging lobe 710, respectively. The zero-lag signal 705appears as more of a plateau than a distinct peak, that possiblyindicates very little material was striking the probe (regardless ofcharge). Accordingly the measured entrainment static data shown in FIG.7 indicates that the positively charged catalyst particles were notsegregating out of the cycle fluid and accumulating onto the innersurfaces of the polymerization system. Hyperfouling of the reactor wasnot observed during this polymerization reactor startup of Example 2.

Referring to Example 3, FIG. 8 is a graphical depiction of measuredentrainment static detected by a particle accumulation probe duringmonitoring of a cycled fluid flowing through a gas phase polymerizationreactor cycle line. The time at which the catalyst was introduced to thepolymerization reactor was around 1.6×10⁴ data points on the x-axis orabout 2 minutes and 40 seconds after measurement of the electric currentbegan.

The polymer product in Example 3 was also prepared by polymerizingethylene and hexene in a gas phase polymerization reactor 101. Thepolymer product was produced using a metallocene catalyst. Theconditions of polymerization were similar to those used in Example 2.After introduction of the catalyst (approximately the 1.6×10⁴ datapoint) a general increase or widening of static detected by the particleaccumulation probe was observed and is clearly shown as a widening ofthe measured static shown in FIG. 8.

FIG. 9 is a graphical depiction of the absolute autocorrelatedentrainment static data shown in FIG. 8. The absolute autocorrelationdata graphically depicted in FIG. 9 shows that an average charge of thecharged particles in the cycle fluid was also negatively charged.However, the average particle contacting the particle accumulation probewas positively charged catalyst particles. FIG. 10 is a close-up view ofthe graphical depiction shown in FIG. 9 focused on a time lag of 0(zero) seconds. At a time lag of 0 (zero) seconds there was a strongsignal peak 1005, which indicates that a large number of chargedparticles struck the probe, and the particles that did strike the probewere, on average, positively charged catalyst particles. The “passingparticles” create a leading lobe 1003 and a lagging lobe 1010 (y-axisvalues of about 2.1 and about 5.3, respectively, consistent with typicalnegatively charged polymer particles. For the purposes of the presentexample, a “significant segregation of charged material” onto the probe(in this case, positively charged catalyst segregating from amajority-negative polymer particles) can refer to a absoluteautocorrelation zero-lag peak which lies outside the band or rangedefined by the leading lobe and the lagging lobe and of the same type(as a maximum or minimum) as the lagging lobe. Accordingly the measuredentrainment static data shown in FIG. 10 indicates that the positivelycharged catalyst particles were segregating out of the cycle fluid andaccumulating onto the inner surfaces of the polymerization system.Hyperfouling of the reactor was observed during this polymerizationreactor startup.

The entrainment static detected during the normal, steady state gasphase polymerization Example 1 provided a clear indication that theobserved entrainment static was accompanied by negatively chargedpolymer particles predominantly contacting the particle accumulationprobe and, as such, neither catalyst particle accumulation norhyperfouling were observed. The entrainment static detected during thepolymerization reactor startup of Example 2 provided an indication thatthe observed entrainment static was accompanied by relatively few (ifany) particles striking the probe or perhaps some positively chargedcatalyst particles were striking the probe, but not a sufficient amountto cause hyperfouling. In other words, the zero-lag signal (plateau) 705indicated that the amount of positively charged catalyst particles, onaverage, striking the particle accumulation probe in Example 2 were notsufficient to cause hyperfouling within the polymerization system. Thisconclusion is based on the fact that the zero-lag signal (plateau) 705did not exceed the band or range of the leading and lagging lobes 703,710. For example, the lagging lobe 710 had a peak value of about 11while the zero-lag signal (plateau) 705 only had a value of about 9,which did not exceed the band or range of the lagging lobe 710.

In contrast, the entrainment static detected during the polymerizationreactor start-up of Example 3 provided a clear indication that theobserved entrainment static was accompanied by positively chargedparticles predominantly contacting the particle accumulation probe and,as such, hyperfouling was observed. The zero-lag signal (peak) 1005 hada absolute autocorrelation value of about 7.5 and significantly exceededthe absolute autocorrelation value of the lagging lobe 1010, which wasabout 5.3. Accordingly, a surprising and unexpected method formonitoring the entrainment static during operation of a gas phasepolymerization system, e.g., steady state operation, start-up,transition periods, and the like, based on the measured entrainmentstatic using a particle accumulation probe has been discovered.Furthermore, a reliable method for determining when entrainment staticis accompanied by predominantly positively charged catalyst particlesstriking the particle accumulation probe has been developed for use inmonitoring a polymerization reactor system. Absolute autocorrelating theentrainment static can provide a visually understandable and usefulindicator as to whether or not catalyst particles are, or are likely tobe, accumulating onto the inner surfaces of the polymerization system.

All numerical values are “about” or “approximately” the indicated value,and take into account experimental error and variations that would beexpected by a person having ordinary skill in the art. All parts,proportions and percentages are by weight unless otherwise indicated.

Various terms have been defined above. To the extent a term used in aclaim is not defined above, it should be given the broadest definitionpersons in the pertinent art have given that term as reflected in atleast one printed publication or issued patent. Furthermore, allpatents, test procedures, and other documents cited in this applicationare fully incorporated by reference to the extent such disclosure is notinconsistent with this application and for all jurisdictions in whichsuch incorporation is permitted.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method for monitoring a particle/fluid mixture, comprising: flowinga mixture comprising charged particles and a fluid past a particleaccumulation probe; measuring electrical signals detected by the probeas some charged particles pass the probe without contacting the probewhile other charged particles contact the probe; manipulating themeasured electrical signal to provide an output; and determining fromthe output if the charged particles contacting the probe have, onaverage, a different charge than the charged particles that pass theprobe without contacting the probe.
 2. The method of claim 1, whereinmanipulating the measured electrical signal comprises using the absoluteautocorrelation method on the measured electrical signal, anddetermining the absolute autocorrelation vector of the electricalsignal.
 3. The method of claim 2, wherein the absolute autocorrelationof the electrical signal comprises an approaching curve, a leavingcurve, and a curve at zero lag time.
 4. The method of claim 1, whereinthe charged particles comprise catalyst particles and polymer particles,and wherein the fluid comprises one or more hydrocarbons.
 5. The methodof claim 1, wherein the charged particles comprise primarily polymerparticles having, on average, a negative charge and a minority ofcatalyst particles having, on average, a positive charge, wherein theoutput indicates the charged particles contacting the probe are, onaverage, negatively charged polymer particles, and wherein the outputindicates that catalyst particles are not segregating out of the mixturein an amount sufficient to cause the formation of agglomerations.
 6. Themethod of claim 1, wherein the charged particles comprise primarilypolymer particles having, on average, a negative charge and a minorityof catalyst particles having, on average, a positive charge, wherein theoutput indicates the charged particles contacting the probe are, onaverage, positively charged catalyst particles, and wherein the outputindicates that the catalyst particles are segregating out of the mixturein an amount sufficient to cause the formation of agglomerations.
 7. Themethod of claim 1, wherein the charged particles comprise primarilypolymer particles having, on average, a positive charge and a minorityof catalyst particles having, on average, a negative charge, wherein theoutput indicates the charged particles contacting the probe are, onaverage, positively charged polymer particles, and wherein the outputindicates that catalyst particles are not segregating out of the mixturein an amount sufficient to cause the formation of agglomerations.
 8. Themethod of claim 1, wherein the charged particles comprise primarilypolymer particles having, on average, a positive charge and a minorityof catalyst particles having, on average, a negative charge, wherein theoutput indicates the charged particles contacting the probe are, onaverage, negatively charged catalyst particles, and wherein the outputindicates that the catalyst particles are segregating out of the mixturein an amount sufficient to cause the formation of agglomerations.
 9. Themethod of claim 1, wherein the charged particles comprise catalystparticles, and said catalyst particles comprise one or more metallocenecatalysts.
 10. The method of claim 1, wherein the flowing mixture islocated within a polymerization system.
 11. The method of claim 1,wherein the flowing mixture is located within a cycle line of a gasphase polymerization reactor.
 12. The method of claim 1, wherein theparticle accumulation probe is in communication with an internal volumeof a polymerization reactor or a cycle line of the polymerizationreactor.
 13. The method of claim 1, further comprising altering one ormore process parameters if the charged particles contacting the probehave, on average, a positive charge.
 14. The method, further comprisingintroducing one or more continuity additives to the mixture if thecharged particles contacting the probe have, on average, a negativecharge.
 15. The method of claim 1, wherein manipulating the measuredelectrical signal is carried out using a processor.
 16. The method ofclaim 1, wherein the electrical signal is measured at a samplingfrequency of about 100 Hz or more.
 17. A system for monitoring aparticle/fluid mixture, comprising: a fluid conveying structure having aflow path for flowing a mixture comprising charged particles and a fluidthrough the fluid conveying structure; a particle accumulation probe incommunication with the flow path and adapted to detect at least oneelectrical signal generated as the charged particles pass the probewithout contacting the probe and as the charged particles contact theprobe; an electrometer in communication with the particle accumulationprobe and adapted to measure the electrical signal detected by theprobe; and a processor in communication with the electrometer, whereinthe processor receives the measured electrical signal, manipulates theelectrical signal, and provides an output indicating (i) whether thecharged particles contacting the probe are, on average, positivelycharged or negatively charged and (ii) whether the charged particlespassing the probe are, on average, positively charged or negativelycharged.
 18. The system of claim 17, wherein the fluid conveyingstructure comprises a polymerization reactor or a cycle line of apolymerization reactor.
 19. The system of claim 17, wherein the fluidconveying structure comprises a gas phase polymerization reactor or acycle line of the gas phase polymerization reactor.
 20. The system ofclaim 17, wherein the particle accumulation probe is configured todetect both positive and negative charges.